This invention relates to a motor or a generator having a movable member on which permanent magnets are disposed.
In a motor or a generator having a movable member on which permanent magnets are disposed, an eddy current is generated on the surface of the permanent magnets due to high frequency components in the magnetic flux. The resulting eddy current loss causes the problem that the temperature of the permanent magnets is increased due to Joule heat produced by the eddy current.
Tokkai Hei 11-4555 published by the Japanese Patent Office in 1999 discloses a permanent magnet motor in which eddy current loss of the permanent magnets is suppressed. Since the magnet has a divided structure in this conventional example, the voltage in a single divided magnet is small. Furthermore the electrical resistance in a single divided magnet is large. Consequently the eddy current loss generated by the overall structure of permanent magnets can be eliminated.
Since the aforementioned conventional example does not take account of the asymmetrical nature of the variation in the flux density applied to the permanent magnet, an eddy current flows into and is concentrated in several of the divided magnets. Thus a large eddy current loss results in those magnets and their temperature increases.
Furthermore in the conventional example, the performance of the motor or generator may be greatly reduced as the magnetic force is reduced as a result of the increase in the number of divisions.
It is therefore an object of this invention to strategically reduce the eddy current loss without a crucial reduction of the magnetic force in a permanent magnet which is used in a motor or a generator having a movable member provided with permanent magnets.
In order to achieve above object, this invention provides a permanent magnet electrical machine used as a motor or as a generator, comprising: a movable member having a permanent magnet, and a stator having a coil which generates an alternating magnetic field to drive the movable member.
In the permanent magnet electrical machine, the alternating magnetic field applies a repulsive force on the permanent magnet, the permanent magnet is divided into a plurality of sections in order to suppress the flow of an eddy current generated by high frequency components in the alternating magnetic field, and at least one of the sections of the permanent magnet has the shape and dimensions which are determined, taking account of the position dependence of the rate of change in the flux density applied to the permanent magnet during fixed-speed operation of the movable member.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.